Heating could be the best way to disinfect N95 masks for reuse

Since the outbreak of the COVID-19 pandemic, N95 face masks have been
in short supply. Health care workers, in particular, desperately need
these masks to protect themselves from the respiratory droplets of
infected patients. But because of the shortage, many have to wear the
same mask repeatedly. Now, researchers reporting in ACS Nano have
tested several methods for disinfecting N95 materials, finding that
heating them preserves their filtration efficiency for 50 cycles of
disinfection.

N95 masks contain a layer of “meltblown” polypropylene fibers that
form a porous, breathable network. To help capture smaller particles
that could slip through the holes, the fibers are electrostatically
charged. The U.S. Centers for Disease Control and Prevention has
recommended several methods for disinfecting N95 masks, such as heating,
ultraviolet (UV) radiation and bleach treatment, but so far they have
not been tested extensively, especially for multiple rounds of
disinfection. Yi Cui and colleagues wanted to compare five of the
methods that could reasonably be used within a hospital setting to see
how mask materials hold up to repeated disinfections.

In this study, instead of analyzing N95 masks — which should be
reserved for health care workers — the researchers examined pieces of
the meltblown fabric used to make these masks. They treated the material
with a particular disinfectant and compared its ability to filter
aerosol particles (resembling respiratory droplets, but lacking
coronavirus) before and after disinfection. The team found that spraying
the fabric with an ethanol or chlorine bleach solution drastically
reduced the filtration efficiency after only one treatment, from about
96% to 56% (ethanol) or 73% (bleach). A single steam treatment
maintained filtration, but five steam treatments led to a sharp decline
in efficiency. UV radiation allowed up to 20 cycles of disinfection;
however, administering the exact dose of UV that kills the virus without
damaging mask materials could be problematic, the researchers note. The
best disinfection method appeared to be heating. For example, heating
at 185 F for 20 minutes allowed the fabric to be treated 50 times
without loss of filtration efficiency. But frequently donning and
removing N95 masks could affect fit, which also impacts performance, the
researchers point out.